(1) Field of the Invention
The present invention relates in general to apparatus for the mounting of electronic instruments or components, and in particular to a new and novel mounting bracket assembly for housing modules containing electronic instruments or components that also provides for heat dissipation and environmental protection.
(2) Description of the Related Art
While advances in electronics have reduced the size and power consumption requirements of many devices used in industry, the need to locate, arrange and mount any given system comprised of these devices has continued. Simplicity of arrangement, ease of initial installation and subsequent removal for service or replacement, efficiency in design (both economic and mechanical) and above all, safety, predominate the concerns facing the designer of a particular system's actual field installation. With the modularization of many electronic components, field installation concerns often center upon locating the various housing modules that contain the electronic devices in openings in a control panel or instrument console. The electronic modules themselves are then electrically interconnected behind the face of the control panel to complete the system. The housing modules themselves are usually made of steel or aluminum sheet metal. To facilitate the utilization of a standardized design, various engineering standards have settled upon certain size housing modules, clearances and panel openings. Such a system of standardized components aids in the interchangeability of hardware and minimizes the total number of configurations required.
Given that the housing modules contain electronic instruments or components (hereinafter referred to as electronics), a major concern in any field installation is to ensure that there is sufficient heat dissipation to prevent damage or destruction of the electronics. The source of this heat is the electronics themselves. This is still a concern notwithstanding the above-mentioned advances in miniaturization and reduction of power consumption requirements, since the miniaturization process itself has led to circuitry and structures of a much denser configuration than previously encountered. Not all electronics generate the same amount of heat during operation. Accordingly, the means employed to handle the problem of heat dissipation will vary depending upon the heat load present. At relatively low levels of heat load, heat dissipation can be handled satisfactorily through radiation and natural convection from the solid walls of the housing modules that contain the electronics. At steady state conditions, the heat generated by the electronics will equal the heat being rejected to the surroundings. This will result in the establishment of certain steady state temperatures for the electronics and the housing modules themselves, which are a function of the materials employed and the ability of the housing module to dissipate heat. If the electronics steady state operating temperature is greater than their design limit, other measures will be necessary. The above-described heat transfer process is "passive" in nature; i.e., other than the structure of the housing module itself, no additional measures are provided to improve the heat dissipation. Of course there are some levels of heat generation that can only be handled by forced cooling with air or other media; these types of aided heat dissipation would be characterized as an "active" design. While the present invention can be used in a forced cooling environment (using air or other gaseous media) the design of such equipment to provide the forced cooling is beyond the scope of the present invention.
Another well-known passive technique to increase the heat dissipation capability of the housing modules is to provide a plurality of openings in the top and bottom sides of the housing modules, thereby allowing natural convection air currents to pass through the housing module (as well as around and along the sides of the housing module) to aid in heat dissipation. While the increased heat dissipation ability of the multiple openings in the top and bottom sides of the housing module is quite evident, certain disadvantages became apparent with such a design. Firstly, by being open on the top, the internal electronics were now exposed to dripping conductive and/or corrosive liquids, or to particles of dirt, debris or other contaminents, that could fall through the openings and damage the electronics contained therein. Secondly, and of equal importance, the potential for electrical shock to an individual working in the vicinity of the housing modules, due to a tool or other conductive projection falling through one of the openings in the housing modules and contacting the electronics within, was increased. In addition, with either of the above two housing module designs, numerous types of mounting apparatus had been used to secure the housing module to the control panel, undoing to an extent the standardization efforts urged by the above mentioned engineering standards. It has thus become desirable to develop a mounting bracket apparatus for housing modules containing electronics that will facilitate the dissipation of heat generated by the electronics while at the same time eliminating the prior art problems of contamination and potential for electrical shock.